Preparation of contamination-free surfaces of III-V semiconductors is important for many potential electronic and optoelectronic applications. Specifically, cleaning the surface of a grown and processed GaAs or AlGaAs layer for subsequent MBE regrowth is essential for the fabrication of device structures employing lateral heterostructures for current injection, carrier confinement or optical confinement. Aside from native oxides, the major contaminants are carbon, oxygen and silicon. Carbon impurities are particularly troublesome because the presence of carbon is related to carrier depletion at the epilayer-substrate interface. Silicon is a common element and is often found as a surface impurity. Silicon contamination arises, for example, from ion sputtering of quartz liners in ECR plasma sources and from SiCl.sub.4 etching gas.